Live media content includes channels or feeds with scheduled content (e.g., premium movie channels) as well as live broadcasts (e.g., sporting events, news, etc.). Unlike video-on-demand (VOD) content, live content may not have a distinct end point and may continue indefinitely. In addition, VOD content may be buffered or otherwise stored in client devices well in advance of the client playhead (i.e., the content fragment currently being rendered by the client). This is typically not the case for live content because of the fact that the delay between the live playhead (i.e., the latest content fragment available) and the client playhead may be only a few seconds, as well as the fact that the live content is often generated in real time and therefore may not yet exist.
An origin stack is the set of transcoding, digital rights management (DRM), and media processing hardware and software resources to generate encoded content for delivery to client devices. Multiple encoders may be configured to encode the same content for redundancy and load balancing purposes. If one of the encoders becomes unreliable, all of the streaming sessions receiving fragments encoded by that encoder need to start receiving fragments encoded by a different encoder. Typically, source media content is received at an origin stack without a time reference and at different times at different encoders operating in parallel. This can result in playback interruptions on a client device as a media server transitions the client from fragments encoded by one encoder to fragments encoded by another.